1. Field of the Invention
The present invention relates to a magnetic disc apparatus which performs recording/regenerating of information by making use of a magnetic means while a magnetic disc is being rotated in a closed casing, and more particularly, to filtering of air in the closed casing.
2. Description of Related Art
FIG. 1 is a perspective view showing the principal part of a conventional magnetic disc apparatus such as similar to the apparatus disclosed in Japanese Patent Application Laid-Open No. 61-198485 (1986). In FIG. 1, reference number 1 designates a magnetic disc for storing information recorded by a magnetic means, and a plurality of which are separated by predetermined spaces in an array fixed to a rotatory shaft 2 of a spindle motor (not shown). A reference number 3 designates an air filter which receives air flow emanating along a recording face of the magnetic disc 1 by rotation thereof so as to filter air. The air filter 3 is provided with both a filter element 3a and a filter case 3b in which the filter element 3a is housed.
The conventional magnetic disc apparatus has been of such constitution that both the plural magnetic discs 1 fixed to the rotatory shaft 2 and the air filter 3 are housed in a closed casing (not shown). In the apparatus the magnetic disc 1 fixed to the rotatory shaft 2 is rotated by energizing the spindle motor, and recording/regenerating of information is carried out by means of a magnetic head (not shown) positioned close to the recording face of the magnetic disc 1. Since the magnetic disc 1 is rotated at high speed, air flow along the recording face thereof makes a magnetic head float slightly above the recording face, whereby a narrow gap between the magnetic head and the recording face is brought about. If any dust rising from bearings of the spindle motor, for example, comes into the narrow gap, the recording face of the magnetic disc 1 or the magnetic head gets damaged. Therefore, dust is adapted to be collected in such a way that the air flow caused by rotation of the magnetic disc 1 is utilized in order to filter air inside the closed casing.
When the magnetic disc 1 is rotated in the direction of the full-line arrow, because of the viscosity of air, there is brought about air flow along the recording face of the magnetic disc 1 in the direction of the broken-line arrow, and one portion of which flows into the air filter 3. Since the filter element 3a of the air filter 3 is an obstacle to the air flow, the air flow has stagnation therein, and, as a result, dynamic pressure thereof is changed to static pressure, whose change brings about a pressure differential in the front and rear of the filter element 3a. By this pressure differential, air is filtered in the filter element 3a, and all dust can be collected. In order to improve the filtering function of the filter element 3a, there is a need to widen the ventilation area of the filter element 3a. In order to meet the need, the filter element 3a, which is bent in a zigzag form, is housed in the filter case 3b. As shown in FIG. 1, the air filter 3 is provided in the vicinity of the outer periphery of the magnetic disc 1 so that the recording face of the magnetic disc 1 is at right angles to the bend lines of the filter element 3a.
In the conventional magnetic disc apparatus as described above, the air flow along the recording face of the magnetic disc 1 by rotation of the magnetic disc 1 flows into the air filter 3. The air flow gets confused because the air flow collides with convex portions of the filter element 3a as seen from the air in flow side of the filter element 3a. As a result, there is a disadvantage in that the static pressure in front of the filter element 3a becomes too uneven to carry out enough filtering.